In 1804, Lewis and Clark, at the behest of President Jefferson, made their famous western journey. But they weren't the only Americans with their eye on the West--Aaron Burr, former vice-president and senator from New York (and a failed candidate for the New York governorship), was plotting to take over the Louisiana Territory. While the exact details of Burr's vision have long been a matter of historical debate, the gist is that he envisioned a separate country, with New Orleans as capital and himself as impresario--with a few important backers, from Andrew Jackson to the Catholic bishop of New Orleans and chief of America's armed forces General James Wilkinson. It is a fascinating tale but one to which Boston journalist Montgomery fails to do justice. Montgomery's portrait of Jefferson is maddeningly inconsistent: he appears at turns indecisive, calculatingly cruel and dim-witted. The puffed-up prose and Montgomery's penchant for the present tense are distracting, and his unconcealed disdain for professional historians will strike the reader as more than a touch defensive. Finally, Montgomery's admission in the last pages of the book that the story he tells here of Burr's wild schemes--a story of something that almost happened, but did not--is ""ultimately irrelevant"" will leave readers who plow through the entire volume wondering why they bothered. (July)